Arctic North Atlantic Research Articles

Middle Miocene ice sheet expansion in the Arctic: Views from the Barents Sea

Revised core data from Ocean Drilling Program (ODP Leg 151, Hole 909C) and preglacial paleorelief and bathymetric reconstructions in the Barents Sea and the Arctic gateway region indicate that large‐scale glaciations were already developed in the northern Barents Sea during the Middle Miocene Climate Transition (MMCT), ∼15–14 million years ago. Our findings show that subsequent to an ice‐free period during the Miocene Climate Optimum (MCO, ∼17–15 Ma), glacially eroded materials from the uplifted northern Barents Sea were transported by iceberg flotillas toward the Fram Strait. The simultaneous opening of the North Atlantic–Arctic gateway provided pathways for iceberg transport from the north. The expansive ice growth is probably induced by both large‐scale changes in ocean circulation due to enhanced flow of Atlantic water into the Arctic Ocean during opening of the gateway and concurrent global cooling during the MMCT.

Arctic Ocean Freshwater Changes over the Past 100 Years and Their Causes

Abstract Recent observations show dramatic changes of the Arctic atmosphere–ice–ocean system. Here the authors demonstrate, through the analysis of a vast collection of previously unsynthesized observational data, that over the twentieth century the central Arctic Ocean became increasingly saltier with a rate of freshwater loss of 239 ± 270 km3 decade−1. In contrast, long-term (1920–2003) freshwater content (FWC) trends over the Siberian shelf show a general freshening tendency with a rate of 29 ± 50 km3 decade−1. These FWC trends are modulated by strong multidecadal variability with sustained and widespread patterns. Associated with this variability, the FWC record shows two periods in the 1920s–30s and in recent decades when the central Arctic Ocean was saltier, and two periods in the earlier century and in the 1940s–70s when it was fresher. The current analysis of potential causes for the recent central Arctic Ocean salinification suggests that the FWC anomalies generated on Arctic shelves (including anomalies resulting from river discharge inputs) and those caused by net atmospheric precipitation were too small to trigger long-term FWC variations in the central Arctic Ocean; to the contrary, they tend to moderate the observed long-term central-basin FWC changes. Variability of the intermediate Atlantic Water did not have apparent impact on changes of the upper–Arctic Ocean water masses. The authors’ estimates suggest that ice production and sustained draining of freshwater from the Arctic Ocean in response to winds are the key contributors to the salinification of the upper Arctic Ocean over recent decades. Strength of the export of Arctic ice and water controls the supply of Arctic freshwater to subpolar basins while the intensity of the Arctic Ocean FWC anomalies is of less importance. Observational data demonstrate striking coherent long-term variations of the key Arctic climate parameters and strong coupling of long-term changes in the Arctic–North Atlantic climate system. Finally, since the high-latitude freshwater plays a crucial role in establishing and regulating global thermohaline circulation, the long-term variations of the freshwater content discussed here should be considered when assessing climate change and variability.

Causes of November cooling of the 1980s–1990s in European Russia

In the 1980s–1990s, a widespread November cooling occurred in European Russia against the background of global warming. Analysis showed that the observed cooling was caused by anomalous cold advection at the eastern edge of the area of positive sea-level pressure and geopotential anomaly centered over Scandinavia and the Gulf of Bothnia. This November circulation pattern is related to the positive phase of the Arctic Oscillation in the preceding winter. It is concluded that the observed November cooling was caused by the prevalence of the positive phase of the wintertime Arctic Oscillation and North Atlantic Oscillation in the last two decades of the 20th century.

Interplay of oceanographic and paleoclimate events with tectonism during middle to late Miocene sedimentation across the southwestern USA

Continental sedimentation reflects a complex interplay of tectonics and climate. A 2000-km transect from coastal California to the western Great Plains documents a major increase in sedimentation (ca. 16–6 Ma) coeval with deposition of the hemipelagic Monterey Formation along the California coast. Basin and Range-style regional extension following elongation of the Pacific–North American transform boundary at ca. 17.5 Ma provided fault-bounded basins for accommodation space, but sedimentation also occurred on unextended erosional surfaces of the Great Plains and Colorado Plateau. Two global climate transitions bracket this sedimentary interval. The middle Miocene transition (ca. 17–12 Ma) records the global change from equatorial to meridional circulation caused by: (1) closing of the eastern Tethys Seaway (ca. 18 Ma); (2) opening of the Arctic–North Atlantic connection (ca. 17.5 Ma); (3) growth of the East Antarctic Ice Sheet (ca. 14 Ma); and (4) closing of the Indonesian Seaway (ca. 12 Ma). Upwelling of cold waters along the California coast, abetted by domination of La Nina phases of El Nino–Southern Oscillation (ENSO), progressively aridified the Southwest as reflected in sedimentary and biologic records. The second climate transition occurred as opening of the Gulf of California (ca. 6 Ma) intensified the North American monsoon, resulting in integration of drainages, incision of uplifts, and exhumation of basin fills. The Miocene ended with the driest climate of the Tertiary (both regional and global) accompanied by conversion of savanna to steppe or scrub desert, spread of C4 grasses, and the greatest mammal extinction of the Neogene.

Revision of Chone Krøyer, 1856 (Polychaeta: Sabellidae) from the eastern central Atlantic and Mediterranean Sea with descriptions of two new species

A neotype specimen is designated for Chone acustica (Claparede, 1870) with a full description. The original descriptions of Chone arenicola Langerhans, 1880 and Chone collaris Langerhans, 1880, both from Madeira, did not include some details and incomplete or misleading information was provided, so both species are redescribed. Amendments to the description of Chone longiseta Giangrande, 1992 are also given together with the methyl green staining pattern of Chone usticensis Giangrande et al. 2006. Two new species are described: Chone gambiae sp. nov., from the Gulf of Naples and Chone dunerificta sp. nov., from the Gulf of Salerno. This study shows the distribution of Chone duneri Kroyer, 1856, and Chone filicaudata Southern, 1914, to be restricted to the Arctic seas and North Atlantic Ocean, respectively. Records from the Mediterranean Sea are found to be erroneous.

North Atlantic–Arctic Mediterranean exchanges in an ensemble hindcast experiment

An ensemble‐hindcast approach is designed to simulate North Atlantic circulation changes during the period 1948–2005 using the Max Plank Institute Ocean Model forced by atmospheric reanalysis data. The experiment seeks to isolate oceanic changes related to the atmospheric forcing history by evaluating the role of initial conditions and masking internal model variability in the ensemble mean results. Characteristics of the complete North Atlantic–Arctic Mediterranean exchange system is described at key sections by time series of exchanges of volume, ice, heat, and liquid freshwater. Volume transports are divided into water masses by properties, and the constructed climatology of exchanges is shown to compare well with available observational estimates of individual branches. In response to the atmospheric forcing history, we find a modest but robust decline of the Atlantic meridional overturning circulation of 0.4 Sv/decade, in total 2–2.5 Sv since 1948. In contrast, overturning exchanges with the North Atlantic and Nordic Seas and with the Nordic Seas and Arctic Ocean show no sign of cessation. A marked increase in the freshwater storage of the Nordic Seas and in particular of the subpolar Atlantic accompany the model decline in Atlantic overturning. The characteristics of the modeled freshening bears similarities with observed patterns of change since the 1950s, but whereas the origin of observed freshening is uncertain, freshening in the model predominantly results from dynamic changes linked to prominent changes in atmospheric circulation. Moreover, documented increase in the drainage of major Arctic‐rivers is found to have a negligible effect on the oceanic changes.

Simulated Arctic Ocean Freshwater Budgets in the Twentieth and Twenty-First Centuries

Abstract The Arctic Ocean freshwater budgets in climate model integrations of the twentieth and twenty-first century are examined. An ensemble of six members of the Community Climate System Model version 3 (CCSM3) is used for the analysis, allowing the anthropogenically forced trends over the integration length to be assessed. Mechanisms driving trends in the budgets are diagnosed, and the implications of changes in the Arctic–North Atlantic exchange on the Labrador Sea and Greenland–Iceland–Norwegian (GIN) Seas properties are discussed. Over the twentieth and the twenty-first centuries, the Arctic freshens as a result of increased river runoff, net precipitation, and decreased ice growth. For many of the budget terms, the maximum 50-yr trends in the time series occur from approximately 1975 to 2025, suggesting that we are currently in the midst of large Arctic change. The total freshwater exchange between the Arctic and North Atlantic increases over the twentieth and twenty-first centuries with decreases in ice export more than compensated for by an increase in the liquid freshwater export. Changes in both the liquid and solid (ice) Fram Strait freshwater fluxes are transported southward by the East Greenland Current and partially removed from the GIN Seas. Nevertheless, reductions in GIN sea ice melt do result from the reduced Fram Strait transport and account for the largest term in the changing ocean surface freshwater fluxes in this region. This counteracts the increased ocean stability due to the warming climate and helps to maintain GIN sea deep-water formation.

Trajectory Shifts in the Arctic and Subarctic Freshwater Cycle

Manifold changes in the freshwater cycle of high-latitude lands and oceans have been reported in the past few years. A synthesis of these changes in freshwater sources and in ocean freshwater storage illustrates the complementary and synoptic temporal pattern and magnitude of these changes over the past 50 years. Increasing river discharge anomalies and excess net precipitation on the ocean contributed approximately 20,000 cubic kilometers of fresh water to the Arctic and high-latitude North Atlantic oceans from lows in the 1960s to highs in the 1990s. Sea ice attrition provided another approximately 15,000 cubic kilometers, and glacial melt added approximately 2000 cubic kilometers. The sum of anomalous inputs from these freshwater sources matched the amount and rate at which fresh water accumulated in the North Atlantic during much of the period from 1965 through 1995. The changes in freshwater inputs and ocean storage occurred in conjunction with the amplifying North Atlantic Oscillation and rising air temperatures. Fresh water may now be accumulating in the Arctic Ocean and will likely be exported southward if and when the North Atlantic Oscillation enters into a new high phase.

Numerical simulation of impurity and fresh water propagation in the Arctic–North Atlantic system

Numerical simulation of impurity and fresh water propagation in the Arctic–North Atlantic system

Numerical modelling of oceanic circulation and sea ice in the North Atlantic–Arctic Ocean–Bering Sea region

Numerical modelling of oceanic circulation and sea ice in the North Atlantic–Arctic Ocean–Bering Sea region

Numerical simulation of impurity and fresh water propagation in the Arctic–North Atlantic system

Numerical simulation of impurity and fresh water propagation in the Arctic–North Atlantic system

Numerical modelling of oceanic circulation and sea ice in the North Atlantic–Arctic Ocean–Bering Sea region

We give the physical statement and numerical algorithms of an original model of oceanic circulation based on splitting over physical processes and geometric coordinates. Splitting makes it possible to effectively realize implicit time integration schemes for transport-diffusion equations. The model uses a vertical σ coordinate. We specify 27 vertical levels with higher resolution in the upper layer and use horizontal resolution 1/3° in latitude and 1/3° in longitude. We model the North Atlantics from 20° S coupled with the Arctic Ocean. The model is written in a rotated spherical coordinate system with its poles beyond the integration domain.We carried out an experiment simulating the climatic annual cycle of oceanic fields characteristics for 12 years taking into account the melting, growth, and drift of oceanic ice. The boundary conditions are given by the OMIP project database. Instead of the stream function we use a sea level function in the model. We compare the model current fields, sea level fields, mass and heat transport through the main straits both with observed data and other authors' simulation results. The model realistically reproduces all large-scale currents and features of the sea level field. The mass transport 5 Sv of the dense saline bottom water from the Greenland Sea to the Atlantic was calculated for the Denmark Strait. We revealed a circulation compensation mechanism for differently directed mass and heat flows in the Atlantic–Arctic exchange processes.

Crustal evolution of Western and Central Europe

Abstract A new Moho depth map has been assembled for Western and Central Europe and the Western Mediterranean area that is exclusively based on published regional Moho depth maps. Tectonic overlays summarize Caledonian and Variscan tectonic units, Permo-Carboniferous fault systems and magmatic provinces, Mesozoic and Cenozoic rift-wrench systems, areas of intraplate compression, the outlines of Alpine orogens and the distribution of oceanic crust. Based on a comparison of these overlays with the Moho depth map we assess processes that controlled the evolution of the crust in the various parts of Europe through time. The present-day crustal configuration of Western and Central Europe results from polyphase Late Palaeozoic to recent lithospheric deformation that overprinted the margin of the Proterozoic East European Craton and particularly the Caledonian and Variscan crustal domains. Following consolidation of the Caledonides, their crustal roots were destroyed in conjunction with Devonian wrench tectonics and back-arc rifting. During the Permo-Carboniferous tectonomagmatic cycle, wrench faulting disrupted the crust of the Variscan Orogen and its foreland and the lithosphere of these regions was thermally destabilized. Late Permian and Mesozoic re-equilibration of the lithosphere-asthenosphere system was interrupted by the development of the Arctic-North Atlantic, Tethyan and associated rift systems. During the Alpine orogenic cycle, intraplate compressional stresses controlled basin inversion-related crustal thickening and lithospheric folding, as well as the evolution of the Rhine-Rhone rift system. Variably deep crustal roots characterize the Alpine orogenic chains. Neogene back-arc extension disrupted the eastern Pyrenees, Betic-Balearic, Apennine and Dinarides orogens.

The relationship between the 0°C isotherm and atmospheric forcing in the Arctic Ocean

Empirical Orthogonal Function (EOF) analysis was performed on the gridded data of the depth to the 0°C isotherm to better understand Atlantic layer variability in the Arctic Ocean. The first mode accounts for 51% of the total variance. The second mode accounts for 26% of the variance, and shows high variability in the region of inflow from the Barents Sea, and large but oppositely signed variability in the region near the Canadian Archipelago and along the path of the Transpolar Drift. This second mode is correlated with the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) indices. Composite analyses of the data using the AO and NAO indices to partition the data reinforces the physical relationship between the second EOF and atmospheric forcing. This study shows that the variability of the Atlantic Layer characterized by the 0°C isotherm across the Arctic Ocean is significantly correlated with atmospheric driving.

Neogene stratigraphy and the sedimentary and oceanographic development of the NW European Atlantic margin

A regional correlation of Neogene stratigraphy has been attempted along and across the NW European Atlantic continental margin, between Mid-Norway and SW Ireland. Two unconformity-bounded successions are recognised. These are referred to as the lower and upper Neogene successions, and have been dated as Miocene–early Pliocene and early Pliocene–Holocene, respectively, in age. Their development is interpreted to reflect plate-wide, tectonically driven changes in the sedimentary, oceanographic and latterly climatic evolution of the NE Atlantic region. The lower Neogene succession mainly preserves a record of deep-water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities, within this succession, on both sides of the eastern Greenland–Scotland Ridge from the mid-Miocene. This is interpreted to record enhanced deep-water exchange through the Faroe Conduit (deepest part of the Southern Gateway), and can be linked to compressive inversion of the Wyville–Thomson Ridge Complex. Thus, a pervasive, interconnected Arctic–North Atlantic deep-water circulation system is a Neogene phenomenon. The upper Neogene succession records a regional change, at about 4 Ma, in the patterns of contourite sedimentation (submarine erosion, new depocentres) coeval with the onset of rapid seaward-progradation of the continental margin by up to 100 km. This build-out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin. Associated changes in deep-water circulation may be part of an Atlantic-wide reorganisation of ocean bottom currents. Glacial sediments form a major component of the prograding shelf margin (shelf-slope) sediment wedges, but stratigraphic data indicate that the onset of progradation pre-dates significant high-latitude glaciation by at least 1 Ma, and expansive Northern Hemisphere glaciation by at least 3 Ma.

Winter Northern Hemisphere surface air temperature variability associated with the Arctic Oscillation and North Atlantic Oscillation

The interannual variability of winter surface air temperature (SAT) in the Northern Hemisphere (NH) associated with the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) is studied. The AO and the NAO show different impacts on winter NH SAT variations. The AO affects the SAT over the Euro‐Asian and African continents, whereas the NAO is more regional with the major effect on the SAT in the western North Africa. This discrepancy can be reflected in other atmospheric variables such as sea level pressure and geopotential height fields as well. The analyses in this paper also suggest that the AO‐related signal can penetrate deeply into the stratosphere while the NAO one is largely a tropospheric phenomenon.

Synsedimentary faults and amalgamated unconformities: Insights from 3D-seismic and core analysis of the Lower Triassic Middle Buntsandstein, Ems Trough, north-western Germany

The Late Permian/Early Triassic succession of the Central European Basin (CEB) was repeatedly affected by the tectonic pulses associated with the earliest phases of Tethyan and Arctic–North Atlantic rifting. Effects of the differential tectonic subsidence are particularly well recorded by unconformities, which form widespread sequence boundaries. Such unconformities are most obvious in areas occupied by fault-controlled intra-basinal highs (swells). In that areas, stratigraphic loss may comprise entire Lower and Middle Buntsandstein formations and in places remnant Middle Buntsandstein successions directly rest on Permian strata. Analysis of 3D-seismic data and well logs combined with high-resolution sedimentological logging of drillcores at the western margin of the Ems Trough (NW Germany) reveals details of synsedimentary tectonic control on sequence development. Early Triassic extensional faulting of basement blocks provided stepwise addition of accommodation space for continental sequences by growth faulting along north–south oriented fault zones blocks on the flanks of the East Netherlands High. This process is most evident during the development of the Hardegsen Unconformity, which is characterised by an amalgamation of succeeding unconformity surfaces in areas of structurally controlled intrabasinal highs.

Formation and pathways of North Atlantic Deep Water in a coupled ice–ocean model of the Arctic–North Atlantic Oceans

We investigate the formation process and pathways of deep water masses in a coupled ice–ocean model of the Arctic and North Atlantic Oceans. The intent is to determine the relative roles of these water masses from the different source regions (Arctic Ocean, Nordic Seas, and Subpolar Atlantic) in the meridional overturning circulation. The model exhibits significant decadal variability in the deep western boundary current and the overturning circulation. We use detailed diagnostics to understand the process of water mass formation in the model and the resulting effects on the North Atlantic overturning circulation. Particular emphasis is given to the multiple sources of North Atlantic Deep Water, the dominant deep water masses of the world ocean. The correct balance of Labrador Sea, Greenland Sea and Norwegian Sea sources is difficult to achieve in climate models, owing to small-scale sinking and convection processes. The global overturning circulation is described as a function of potential temperature and salinity, which more clearly signifies dynamical processes and clarifies resolution problems inherent to the high latitude oceans. We find that fluxes of deep water masses through various passages in the model are higher than observed estimates. Despite the excessive volume flux, the Nordic Seas overflow waters are diluted by strong mixing and enter the Labrador Sea at a lighter density. Through strong subpolar convection, these waters along with other North Atlantic water masses are converted into the densest waters [similar density to Antarctic Bottom Water (AABW)] in the North Atlantic. We describe the diminished role of salinity in the Labrador Sea, where a shortage of buoyant surface water (or excess of high salinity water) leads to overly strong convection. The result is that the Atlantic overturning circulation in the model is very sensitive to the surface heat flux in the Labrador Sea and hence is correlated with the North Atlantic Oscillation. As strong subpolar convection is found in other models, we discuss broader implications.

Linearity of the Atmospheric Response to North Atlantic SST and Sea Ice Anomalies

Abstract The observations of the ocean–atmosphere–sea ice have recently revealed that the oceanic surfaces can have a subtle but significant impact on the atmospheric long-term fluctuations. Low-frequency variations and long-term trends of the North Atlantic atmospheric circulation have been partly related to particular SST and sea ice features. In this work, the influence of typical tripolar SST and dipolar sea ice anomalies in the North Atlantic–Arctic on the atmosphere is investigated. A large ensemble of AGCM simulations forced by three different anomalous boundary conditions (SST, sea ice, and SST + sea ice) are used. The linearity of the simulated response in the winter season is particularly assessed. In these experiments, while the winter low-level temperature response is mainly symmetric about the sign of the forcing, the asymmetric part of the geopotential response is substantial. The sea ice forcing maintains a baroclinic response with a strong temperature anomaly in the vicinity of the forcing but with a weak vertical penetration. The SST maintains an NAO-like equivalent barotropic temperature and geopotential height response that extends throughout the troposphere. It is also shown that the combination of the two forcings is mainly linear for the low-level temperature and nonlinear for the geopotential height. While the SST forcing seems to be the main contributor to the total temperature and geopotential height responses, the sea ice forcing appears to introduce significant nonlinear perturbations.

On distributional responses of North Atlantic fish to climate change

Abstract Changes in fish distribution and climate in the North Atlantic have been observed for millennia by seafaring peoples, chronicled in many historical anecdotes, and recently studied systematically. For temperate to Arctic North Atlantic fish, a literature compendium of limits of temperature, salinity, and depth during feeding and spawning was used to investigate factors that influence distribution. Latitude and depth were negatively correlated with species number and density. Peak numbers of species feed at 0–4°C, but spawn at 2–7°C and salinities of 32.5–33.5. Principal components of feeding depths and temperatures suggested four groups of species: (i) small pelagics characterized by shallow habitat and cooler temperatures; (ii) most groundfish in deeper and warmer waters; (iii) warm-water large pelagics; and (iv) deepwater species. Spawning temperatures, salinities, depths, and timing produced groupings consistent with feeding components for pelagics, but differing for distant migrants such as tunas. Principal components (PCA) of spawning characteristics explained 56% of the variance in species resilience (doubling time), while PCA of feeding characteristics explained only 23%. We infer that the small pelagics capelin (Mallotus villosus) and herring (Clupea harengus) react strongly and quickly to climate change because of their physiological limits and potential for fast population growth. Verification comes from Icelandic and Greenland waters, which warmed considerably during 1920–1940, and where capelin, herring, cod (Gadus morhua), and other species shifted north very quickly.